#include <stdio.h>

//hmean()函数定义处
int hmean(const int x, const int y, float* r)
{
    double z=0;
    if(x+y==0) return 0;
    z=(2.0*x*y)/(x+y);
    *r=z;
    return 1;
};

int main()
{
    int x=0,y=0;
    scanf("%d %d",&x,&y);

    float r = 0;
    int b = hmean(x,y,&r);

    if (b)
        printf("hmean(%d,%d)=%.2f",x,y,r);
    else
        printf("Input error.");

    return 0;
}
